The Scientific Evidence

Some mental health campaigners have claimed that the association between violence with mental illness is ‘modest’, or non-existent.

Some even claim it is a ‘myth’.

Consistent evidence from many international scientific studies shows this view is incorrect. The association between mental illness and violence is actually of the same order as that between smoking and cancer.

32 INTERNATIONAL SCIENTIFIC STUDIES 1981 – 2009

1. In 1981, Petursson and Gudjonsson studied all homicide offenders In Iceland
between 1900 – 1979 and found a third were psychotic or mentally disordered.[1]

More than half the people convicted of a homicide… had a major mental disorder

2. A study by Taylor & Gunn in 1984 in Greater London prisons found offenders had a high rate of psychiatric disorder. Those convicted of homicide had a substantially higher prevalence
of schizophrenia than would be expected from the general population.[2]

23% of homicide offenders were psychotic at the time of the offence

3. In 1986 in Northern Sweden an investigation by Lindqvist found more than half the people convicted of a homicide between 1970 and 1981 had
a major mental disorder.[3]

4. In Copenhagen in 1987 an in-depth study by Gottlieb, Gabrielsen and Kramp of all those convicted of homicide over a 25 year period found 23% of homicide
offenders were psychotic at the time of the offence.[4]

5. In the United States in 1990 Swanson investigated a community based sample of 10,000 and asked people if they had committed any violent action over the last 12 months. Violence was reported by 2% of those with no psychiatric diagnosis, by 8% of those with pure schizophrenia, and by 13% of those whose
schizophrenia was complicated by substance misuse or personality disorder.[5]

The violent crime rate for schizophrenics was four times higher than for non-patients

6. The same year in Sweden, Lindqvist and Allebeck followed 644 schizophrenic patients over 14 years and confirmed the violent crime rate for schizophrenics was four times higher than for non-patients. They
also showed how risk was increased by drugs and alcohol.[6]

Men with major mental health disorders were four times more likely to be registered for violent offences than those with no such disorder

7. Two years later in another large Swedish study, Hodgins, found men with major mental health disorders were four times more likely to be registered for violent offences than those with no such disorder.[7]

Psychotic patient group had higher rates on all measures of violent/illegal behavior

8. In New York in 1992, Link, Andrews & Cullen compared arrests and reported violence for two different groups – one of patients with a mental health problem , the other never having had MH treatment. They found the psychotic patient group had higher
rates on all measures of violent/illegal behavior,[8]

35% of homicide offenders met lifetime criteria for a major mental disorder

9. Also in 1992 this time in Canada, a study by Cote and Hodgins found some 35% of homicide offenders met lifetime
criteria for a major mental disorder.[9]

10. In the United States in 1993 Lidz, Mulvey & Gardner – followed up 357 patients in a psychiatric emergency room for six months – and found 45% of all
cases went on to commit violent acts.[10]

Significant increased risk of homicidal violence

11. Finnish studies by Erohnen, Tiihonen and Hakola 1996 (a and b) of 693 homicide offenders over eight years found significant increased risk of homicidal violence by people with
schizophrenia - 10 times greater risk than for the general population.[11]

Significantly more likely to be arrested for criminal violence

12. Danish studies of 400,000 people born between 1944 and 1947 showed a distinct association between schizophrenia and violence. People with psychosis orschizophrenia were significantly more likely to be arrested for criminal violence than people who had never been hospitalized (Hodgins et al 1996, Brennan et al 2000).[12]

13. In 1997 in Israel, a study by Stueve & Link found psychotic disorder
increased the risk of fighting and use of weapons.[13]

The risk of criminal behaviour was significantly higher among people with psychotic disorders

14. The same year a large scale study examining 12,000 people in North Finland over 26 years, Tiihonen et al 1997, found the risk of criminal behaviour was significantly higher among people with psychotic disorders, In particular they found those with alcohol-induced psychoses and schizophrenics with coexisting substances abuse had a higher risk for violent
behaviour.[14]

People with schizophrenia and other psychotic disorders are significantly more likely to commit violent acts than other members of the population

15. In 1998 a European study, Eronen, Angemeyer & Schulze 1998, reported people with schizophrenia and other psychotic disorders were significantly more likely to commit violent acts than other members of the population.[15]

Schizophrenia was most strongly associated with personal violence

16. The same year, a British study, Taylor et al 1998, examined the association between mental disorder and violence in a survey of 1740 patients resident in a high security hospital. They found Schizophrenia was most strongly associated with personal violence. The found more than 75% of those with a psychosis were driven to offend by their delusions.[16]

17. Also in 1998 Belfrage followed up more than a thousand schizophrenic or psychotic patients in Stockholm ten years after their discharge from hospital, and found more than 40% had received a criminal convictions, mostly for
violent crimes. The rate for the general population was less than 10%. [17]

Substantial rates of mental disorder in people convicted of homicide

18. In 1999, a British study by Shaw et al, found substantial rates of mental disorder in people convicted of homicide. They found 14% of perpetrators had symptoms of mental
illness at the time of the offence.[18]

More than a quarter of discharged psychiatric patients committed an act of serious violence within a year of their release.

19. In 2000, the MacArthur Violence Risk Assessment study in the United States, of 951 recently released psychiatric patients found more than quarter (27%) committed an act of serious violence (battery resulting in physical injury, sexual assault, assault involving the use of a weapon, or threat made with weapon in hand) within a year of their release.[19]

20. In New Zealand in 2000, Arsenault et al studied 961 young adults in Dunedin between 1972-73, and found In the age group committing most violent incidents, people with mental disorders accounted for a considerable amount of violence in the community. They found 10% of violence risk was uniquely
attributable to people with schizophrenia or similar disorders.[20]

A quarter of patients reported thoughts of violence directed at specific individuals. Nearly 1 in 10 admitted to owning weapons

21. In Britain, a study by Sanders et al examined 114 patients admitted to a general psychiatric ward in Middlesbrough found that almost a quarter of patients reported thoughts of violence directed at specific individuals. Nearly 1 in 10 admitted
to owning weapons and one in 20 to carrying them.[21]

22. The following year a landmark investigation in Britain by Walsh et al, of 700 psychotic patients found that 22% participants physically assaulted another person within the two years of the study.[22]

It is now accepted that people with schizophrenia are significantly more likely to be violent than other members of the general population

23. A study by the same researchers in 2002 in the British Journal of Psychiatry noted “It is now accepted that people with schizophrenia are significantly more likely to be violent than other members of the general population.”[23]

In countries with relatively low crime rates, the crimes committed by the mentally ill, particularly violent crimes, represent a significant proportion of all crimes

24. That same year a landmark study of more than 15,000 people in Stockholm, Hodgins & Janson, found a distinct association between mental illness and crimes of violence. They found in countries with relatively low crime rates, the crimes committed by the mentally ill, particularly violent crimes, represent a significant
proportion of all crimes.[24]

Increased likelihood of homicide

25. In 2004 in Austria a major 25 year study of 1087 homicide perpetrators by Schanda et al. found Major Mental Disorders were associated with an increased likelihood of homicide (two-fold in men and six-fold in women). They confirmed the risk was
increased if the patients also abused drugs and or alcohol.[25]

90% of people convicted for homicide had a psychiatric diagnosis, with nearly 20% having a psychotic illness

26. Also in 2004 a major Swedish study by Fazel & Grann of more than 2000 people convicted of homicide or attempted homicide between 1988 and 2001, found 90% of people convicted for homicide had a psychiatric diagnosis, with nearly 20% having a psychotic illness.[26]

Significant levels of violence

27. The same year a study by Soyka et al, in Germany found significant levels of violence (particularly physical assault) in 1700 schizophrenic patients following their release from hospital.[27]

28. Also that year a landmark study by Wallace, Mullen & Burgess in Victoria, Australia following 2861 patients with schizophrenia over a 25 year period found a significant association between schizophrenia and a higher rate of criminal convictions, particularly for violent offences.[28]

29. In 2006 a nationwide study of 1410 schizophrenic patients across the United States by Swanson et al found 19% were involved with some form of violent behaviour with nearly 4% committing acts serious violence over a six month period. Serious violence was associated with psychotic and depressive symptoms, childhood conduct problems, and victimization.[29]

People with schizophrenia make a significant contribution to violence in our communities. There is a substantial and clinically relevant association between schizophrenia and violence.

30. Also in 2006, another major study by Paul Mullen in Australia wrote that “People with schizophrenia make a significant contribution to violence in our communities” He said there is “a substantial and clinically relevant association” between schizophrenia and violence and that “the 10% or so from which will emerge the perpetrators of most of the serious violence are identifiable in advance”.[30]

“In scientific terms the existence of a link between mental disorder and violence is no longer controversial, [it is] of a similar order of magnitude to the association between smoking and lung cancer.”

31. In 2007 in his book ‘Treating Violence’ Professor Tony Maden, Professor of Forensic Psychiatry at Imperial College and Consultant Psychiatrist at Broadmoor High security hospital wrote – “In scientific terms the existence of a link between mental disorder and violence is no longer controversial… There is a highly significant association between psychotic mental illness and violence in the community, of a similar order of magnitude to the association between smoking and lung cancer.”[31]

This association between schizophrenia and violent offending is robust

32. Finally in 2008, Sheilagh Hodgins summed up the level of research on schizophrenia and violence when she wrote

“This association between schizophrenia and violent offending is robust: it has been observed by different research teams who recruited samples from countries with different cultures and health and justice systems, and who measured the association of schizophrenia and offending using different experimental designs including longitudinal investigations of birth and population cohorts, comparisons of people with schizophrenia and their neighbours, and diagnostic studies of random samples of convicted offenders.”[32]

SOURCES

Previous claims

Prof Pamela Taylor calls the association between mental illness and violence “modest” NHS National Programme on Forensic Mental Health Research. Mental Illness and Serious Harm to others. (nd) Page 8

“Myth” quote is from Time to Change campaign
http://www.time-to-change.org.uk/what-we-are-doing/our-campaign/summer-2009/summer-campaign-q

STUDY REFERENCES